Language bindings will have problems with raise() and lower() bein in both
ClutterContainer and ClutterActor; hence, this patch renames
clutter_container_raise() and clutter_container_lower() to
clutter_container_raise_child() and clutter_container_lower_child(),
respectively.
Since ClutterActor directly calls ClutterGroup methods we need ClutterContainer
to provide them, so that every container actor behaves the same way.
This patch makes ::raise, ::lower and ::sort_depth_order virtual functions
of the ClutterContainer interface, implemented by ClutterGroup.
The documentation has been added and deprecation warnings have been added
as well.
Finding a child by its ID is a method that should be used by every container
and not only by ClutterGroup. This is needed to actually fix the picking in
ClutterStage.
